Storage and Data

// the API signs; the browser uploads straight to the bucket; the API never touches the bytes
import { S3Client, PutObjectCommand } from '@aws-sdk/client-s3';
import { getSignedUrl } from '@aws-sdk/s3-request-presigner';

const s3 = new S3Client({ region: 'eu-west-1' });
export async function presignKycUpload(userId: string, contentType: 'image/jpeg' | 'image/png') {
  const key = `kyc/${userId}/${crypto.randomUUID()}`;
  const url = await getSignedUrl(s3, new PutObjectCommand({
    Bucket: 'acme-kyc-private', Key: key, ContentType: contentType,
    ServerSideEncryption: 'aws:kms',
  }), { expiresIn: 300 });                       // 5 minutes, one object, one content type
  return { url, key };
}

// browser
await fetch(url, { method: 'PUT', headers: { 'Content-Type': file.type }, body: file });

// an idempotent SQS consumer: the message id is the dedupe key
for (const msg of batch.Records) {
  const { id: eventId, accountId, amountKobo } = JSON.parse(msg.body);
  await db.tx(async t => {
    const seen = await t.oneOrNone('INSERT INTO processed_events(id) VALUES ($1) ON CONFLICT DO NOTHING RETURNING id', [eventId]);
    if (!seen) return;                                   // already applied: ack and move on
    await t.none('UPDATE wallets SET pending_kobo = pending_kobo + $2 WHERE account_id = $1', [accountId, amountKobo]);
  });
}
// throwing here leaves the message to reappear after the visibility timeout;
// after maxReceiveCount it lands in the DLQ with an alarm on its depth